The present invention relates generally to integrated acceleration and angular rate sensors (“multi-sensors”), and more specifically to a silicon micro-machined multi-sensor capable of providing 2-axes of acceleration sensing and 1-axis of angular rate sensing.
Silicon micro-machined multi-sensors are known that comprise at least one accelerometer for providing an indication of acceleration sensing and/or angular rate sensing in a single sensor device. A conventional silicon micro-machined multi-sensor, such as the silicon micro-machined multi-sensor described in U.S. Pat. No. 5,392,650 issued Feb. 28, 1995 entitled MICRO-MACHINED ACCELEROMETER GYROSCOPE, comprises a pair of accelerometers, in which each accelerometer includes a respective accelerometer frame and a respective proof mass suspended from the frame by a plurality of flexures. The conventional micro-machined multi-sensor has a single acceleration-sensing axis, and a single rotation-sensing axis perpendicular to the acceleration axis, associated therewith. Further, the conventional micro-machined multi-sensor is configured to vibrate the respective proof masses in antiphase along a vibration axis, which is perpendicular to the acceleration and rotation axes.
In a typical mode of operation, the conventional silicon micro-machined multi-sensor balances forces of linear acceleration upon the respective proof masses by a first set of electrical restoring forces, which are a function of the linear acceleration of the proof mass along the acceleration axis. The conventional micro-machined multi-sensor is further configured to balance Coriolis forces upon the respective proof masses by a second set of electrical restoring forces, which are a function of the Coriolis acceleration of the proof mass along an axis perpendicular to the rotation and vibration axes. The Coriolis acceleration of each of the proof masses results from the combination of the vibration of the proof masses along the vibration axis, and an applied angular rotation of the proof masses about the rotation axis.
Because the proof masses included in the conventional silicon micro-machined multi-sensor are typically made to vibrate in antiphase, the responses of the proof masses to linear acceleration are in phase, while the responses of the proof masses to Coriolis acceleration are in antiphase. Accordingly, the conventional micro-machined multi-sensor is configured to add the outputs of the respective accelerometers to extract information corresponding to the linear acceleration (i.e., the acceleration sensing information), and to subtract the respective accelerometer outputs to extract information corresponding to the Coriolis acceleration (i.e., the angular rate sensing information).
The above-described conventional micro-machined multi-sensor is typically fabricated separately from its electronics by a process known as bulk micro-machining, which is a relatively expensive process for fabricating micro-machined devices. There are other micro-machining fabrication processes that are generally less expensive than bulk micro-machining such as surface micro-machining with integrated electronics. For example, a conventional surface micro-machined gyroscope is described in U.S. Pat. No. 6,122,961 issued Sep. 26, 2000 entitled MICRO-MACHINED GYROS. That conventional micro-machined gyroscope device may be configured to add as well as subtract the outputs of its Coriolis accelerometers to yield an axis of linear acceleration in the plane of the substrate (i.e., tilt), and a gyroscopic axis perpendicular to the substrate plane (i.e., yaw).
However, the above-described conventional surface micro-machined gyroscope also has drawbacks. For example, the proof masses included therein are suspended from separate accelerometer frames. As a result, there is typically at least a slight mismatch in the resonant frequencies of the respective proof masses, which can make it difficult to generate sufficient drive for vibrating the proof masses at velocities high enough to obtain detectable Coriolis accelerations. Further, having separate accelerometer frames in the micro-machined multi-sensor device generally makes it harder to center the device on a die. Distortions in the die surface area may therefore be asymmetrical relative to the micro-machined device, which can degrade the overall performance of the multi-sensor. Another drawback is that this device generally provides only 1-axis of accelerometer tilt sensing and/or 1-axis of gyroscopic yaw sensing. However, it is often advantageous to have more than one axis of acceleration and/or rate sensing in a single sensor device.
It would therefore be desirable to have a silicon micro-machined multi-sensor that provides more than one axis of acceleration sensing and/or angular rate sensing, and avoids the drawbacks of the above-described conventional micro-machined multi-sensors.